Process of making chromous chlorid



M. C. TAYLOR. PROCESS OF MAKING CHROMOUS CHLORID- APPLICATION FILED 0c'.15,.1919.' 1,369,204. Patented Feb 22, 1921.

2 SHEETS-SHEET 1- M. C. TAYLOR. PROCESS OF MAKING CHROMOUS CHLORID.

APPLICATION FILED DEG 15.1919.

2 SHEETSSHEET Patented Feb. 22,1921.

INVENTOR.

UNITED STATES PATENT "OFFICE.

MAURICE C. TAYLOR, 0F NIAGARA FALLS, NEW YORK, ASSIGNOR. TO NEWTON D BAKER, SECRETARY OF WAR, TRUSTEE.

PROCESS OF MAKING CHROMOUS CHLOIBID.

Specification of Letters Patent.

Application filed December 15, 1919. Serial No. 345,034.

(FILED UNDER, THE ACT OF MARCH 8, 1883, 22 STAT..L., 825;)-

To all whom it. may concern:

Be it known that I, MAURICE-O. TAYLoB,

a citizen of the United States, stationed at I in the United States, without payment of any royalty thereon.

This invention relates to a processfor the electrolytic reduction of chromic chlorid to the divalent salt in which process a high current efficiency is maintained, based upon the principle that the proper amount of current to employ for this electrolysis is a function of the chromicion concentration.

Among the objects of this invention is the production of chromous chlorid from chromic chlorid by having proper concentration of electrolyte; conducting the electrolysis in a two compartment cell havin a spongy lead cathode; automatically regudating the flow of chromic chlorid into the electrolytic cell by the pressure of the hydrogen evolved from the electrolysis; continuousl drawing off the chromous chlorid produce thus making the process a continuous one, if desired.

The current used in this electrolysis serves only as a means of producing nascent hydrogen which is the real reducing agent. If the current produces more hydrogen than is consumed in changing the chromium from the trivalent to the divalent salt, the excess hydrogen will be evolved in gaseous form and serve as a measure of the inefiiciency of current used. The amount of current required at any particular time depends upon the velocity of the reduction reaction of the chromium chlorid to chromous chlorid.

When the amperage is such that gaseous hydrogen is being evolved, there is present in the reactin zone on or nearthe' surface of the electro e, a constant and'never failing excess of nascent hydrogen, which, not being used, is transformed into gaseous hydrogen and evolved. .Under such conditions, the yelocity of reduction, according to the law of mass action depends, not on the amount of nascent hydrogen which varies with the :of chromic chlorid into the cell,

current, but on the concentration of. the chromlc 1011 present in the system.

As long'as there is asufiicient amperage to glve an appreciable evolution of hydrogen (about 3 or 4% of that which would be evolved were none of the hydrogen used for reductlon purposes) the speed of the reduction is not lncreased by increasing the amount of current. Also, if the amount of current is increased, the efiiciency is decreased. In the reduction process of this inventlon, the amperage is so regulated that the evolution of hydrogen is not in excess of 3 or 4% of the amount which would be evolved if none of it were used for reduction purposes. Operating in this way, it is found that the current density usually varies from 3 amper'es per square decimeter when little or no chromous ion is present down to one ampere per square decimeter when 8090% of the chromium has been reduced.

In carrying out this reduction process the current should be regulated, as directed ab'ove, until the cathode solution has [been suiiiciently'v reducedto meet the particular requirements. Then the amperage should be maintained steady and, as thehydro en flow increases, fresh chromic chlorid so u- Patented Feb. 22, 1921.

tion should be added to the cell. At the same time a corresponding amount of chrom'ous chlorid should be removed as finished product. The addition of fresh chromic chlorid will increase the concentration of the trivalent chromium and therefore the velocity of reduction will be increased,- thus using up the excess hydrogen previously evolved.

Referring to the drawings, Figure 1 is a device for automatically regulatin the flowig. 2 is a ctionalview of one form of cell which may e used in carrying out the process. The

flow regulating apparatus-consists of the flow-meter (1) having mercury (53) at the U-tube connected thereto.

bottom of the On. one-side of the U-tube there are a series of contact points A, B, O, D, and E, in

which are sealed platinum ,wires (having their other terminals in the contact points A B C D 'and E of a switch (3). These platinum wires are. connected singly in series with an electromagnet (4), a storagebattery (5) an'da' contact (6) atthe bottom of the U-tnbe containing the mercury (2). .A stora e batteryshupplging 5;].0tvolts' e e con ac arm is'usuallysu 'cient. t

(.7) of the switch is at B, as shown in the drawing, it will' be necessary for. the mercury in the manometer to reach the contact B, before the circuit is closed. When this occurs, the electromagnet will attract the arm (8) thereby throwing in a switch ('9) which will start the motor t10), connected to 'a pump (11), which Supplies chromic chlorid-to the cell. As the chromic chlorid is fed to the cell the hydrogen evolved will be used in reducing the chromic chlorid to chromous chlorid and the pressure of the hydrogen will fall off, consequently, the

. mercury in the, manometer will. drop thus ode chamber which contains the spongylead cathode E, arranged in .theform of abreaking the circuit containin the electromagnet, which in turn will t row out the switch (9) and stop the motor and, consequently, the flow of chromic chlorid into the cell. I

By manipulating the arm (7) of the contact switch, the pressure which the evolved.

hydrogen should reach before the circuit containing the electromagnet is closed may be regulated, thus permitting a satisfactory control of the supply of chromic chlorid to the cell. It will be seen that this controlof chromic chlorid inflow by the hydrogen evolved is automatic. While the chromic chlorid-is bein pumped into the cell as outlined above, t e chromous chloridmay be allowed to flow off as .a finished product,

through a vU-tu'bei connected to the electro lytic'cell in such a way as to maintain the solution bein reduced in the cell at the desired level. if desired, the withdrawal of the chromous chlorid solution may be concathode. The cell as illustrated in Fig.- 2,

consists of a cathode chamber A,'s'urrounded by the anode compartment B from which it is separated byzthe porous wall C. A plu-' rality of carbon anodes. D surround the cathspiral in order to allow free circulation of the cathode solution. A stirrer F is pro- .vided in order that. the solution maybe a tated. The strong hydrochloridacid so ution necessary to maintain the acid content of the anode com artment' enters by wayof the pipe G; pipe is arranged so as to alat all low for the overflow of a small amount of anode liquor while adding the strong hydrochloric acid. yThis overflow-of liquor obtained at H can be strengthened and re- '-tu'rned to the cell if desired. The chlorin es.- c'apes 'by way ofthe gas. exitJ When the automatic device for regulating the flow is employed the hydrogen running to the flowmeter is obtained from the pipe K, and this regulates the chromic chlorid-inflow to the cell at L. M is an overflow pipe forthe chro= Incas chlorid solution produced, which'soluti on must, of course, be protected from the an. should/be gasti ht, the former in order to carry away the c lorin producedand the latter to make possible the measurement or regulation of the pressure of the hydrogen evolved, which pressure isnecessary for the control of the supply of chromic chlorid to the cell by means shown above.

Although the preparation of the chromic I chlorid solutionused in this process is no Both the anode and cathode chambers part of this invention, it is recommended that the preparation be made by reducing chromic anhydrid (010,) with hot concentrated HCl solution. When chlorin is no longer evolved, theliquid is cooled and HCl gas passed in, thus precipitatin the'chromic chlorid in crystaline form. he crystals are washed with dry acetone .until' nearly free from acid. The'prodlict is the green modification of chromic chlorid and ,is readily soluble in water, thus making possible the use of very concentrated solutions for electrolysis. 1

' An alternative but less satisfactory method for obtaining'suitable solutions of chromic chlorid is to heat carbon-and chromic 'oxid (Cr O in a current of chlorin. Chromic chlorid will be deposited as violet scales quite soluble in water containing a trace of chromous chlorld. Y

It isv'ery important that the chromic'ohl'oi-j rid solution be very strong as the best eflicienciesare obtained from solutions con taining 350-500 grams of chromic chlorid per liter. tained with crystals prepared from the anhydrid by the method recommended and outlined above. It. is also important that theacid content 6f the chromic. chlorid solution. benot over 70-80 grams otHCl perliter 'and concentrations as low as 10 20 grams of HCl 'er liter or 12% acid are recommend ed. f course, reduction will takeplace in more dilute or more acid solution but not with best efiicieney. r

This strength-can beeasily ob- The anode chamber is-fill'ed' with solution and is maintained at a gravity of 1.02 to 1.04 which is a solution eontaining v67% of HCl by weight.-

' The resistance of this cell that a tension of 3 or 4 volts is sufiicient to same-lite as. i

. give-the required current? density; It islso reducing a solution of chromic chlorid mand in view of the numero .which may be eifected therein without .der parting from the spirit and scope ofthis invention, it is desired that only such limi- 'tations be imposed as are indicated in the recommendedthat the reductions be made Chromous chloridsolution prepared by this process is especially applicable in converting acetylene toethylene without the production of any ethane. It may alsobe used for reducing other organic compounds such as the reduction ofmaleic or fumaric aclds to succlnlcacldv The present lnvention 1s not 11m1ted to the specific details set forth in the ioregoing examples which should be construed as illustrative and not by way of limitation, modifications appended claims.

I claim as my invention;

1. A process comprising passing an elec-' tric current through a solution of chromic chlorid containing from 12% free hydrochloric acid in a cell having separate anode and cathode compartments until the chic-,-

mic chlorid is reduced to chromous chlorid.

'2. A processcomprising passing an electricjcurrent through a solution of chromic chlorid in a two compartment cell until the chromic chlorid is changed 'to chromous chlorid.

3. A process comprising passing an electric current through a' solution of chromic chlorid in a two compartment cell using a Jspongy lead cathode until the chromic ch10- rid is changed to chromous chlorid. 4. A process comprising passing an electric current through a solution of chromic chloridcontaining free hydrochloric" acid in a twocompartment cell using a cathode of spongy lead until the chromic chlorid-- is changed to chromous chlorid. 5. A process comprising electrolytically a two compartment-cellhaving a cathode 1 of the hydrogen evolved.

of spon lead andagitating the solution durin t e electrolysis.

6. process comprising electrolytically reducing a solution of chromic chlorid contaming 12% of free hydrochloric acid in a two compartment cell having a cathodeof spongy lead and agitating the solution during, the electrolysis. I

7. process comprising passing an electric current throu ha concentrated solution of chromic-c orid' in a cell having separate anode and cathode compartments -until the chromicchlorid is. reduced to' chromous chlorid. v 4

.8. A- process comprising passing an electric current through a solution containing 350-500 gramsof chromic chlorid per liter and a small amount of free hydrochloric acid in a cell having separate anode and cathode compartments until the chromic chlorid is reduced to chromous chlorid.-

. 9. A'process comprising passing an electric current througha-solution containing 350-500 grams of chromic chlorid per liter and a small amount of free hydrochloric acid in. a two compartment cell using a spongy lead cathode until the chromic chlog v rid is reduced to chromous chlorid.

u 10. A continuous .process for making chromous chlorid comprising electrolyzing a solution of chromic chlorid in a cell haVF ing separate anode and cathode compartments and regulating the flow of chromic chlorid into 'the electrolytic -cell'by means 11. A continuous process for making chromous chlorid comprising electrolyzing a concentrated solution of chromic'chlorid using a spongy lead cathode, stirring the solution during electrolysis and automatievolved. 12..A process of reducing chromic chlorid to chromous chlorid consisting in pass- 65 I containing a small amount of free "hydro- =chloric acid, in a two compartment cell,

cally regulating the flow ofchro mic chlorid into the electrolytic cell by the hydrogen ing an electric current through a chromic chlorid solution in a cell having separate anode and cathode compartments, the am-.

perage of said current being such as will 've an evolution of hydrogen equal to 34% of the total hydrogen which would I be evolved by said current if none of the hydrogen were used for-reduction.

MAURICE CITAYLOR. 

